You won't find anything that can power these at those price levels.
The HD6XX needs a strong chain to be built around it. If you don't have the chain or don't want to get it, it's actually not very good, in fact it will sound far worse than other headphones around that price range.
In a pinch, you can just grab an amp. Get the Magni 2 Uber, it should be right around your price range. It won't fully power these either, but it will do about as solid a job as you can get at that range.